Why this DropdownMenu doesn't work in WPF - wpf

Question

I'm trying to make a DropdownMenu in WPF with the code-behind in VB. For any reason that I can't realise this DropdownMenu is not working as I would like to.
This is the MainWindow.xaml file:
<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
mc:Ignorable="d" Height="600" Width="1080" Foreground="White" ResizeMode="NoResize" WindowStartupLocation="CenterScreen" WindowStyle="None">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="250"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<materialDesign:ColorZone Mode="PrimaryMid" Grid.ColumnSpan="2" HorizontalAlignment="Stretch">
<Grid>
<materialDesign:PopupBox PlacementMode="BottomAndAlignRightEdges" HorizontalAlignment="Right" Margin="10"/>
</Grid>
</materialDesign:ColorZone>
<Grid HorizontalAlignment="Stretch" Grid.Row="1" Background="{StaticResource PrimaryHueMidBrush}">
<Grid.RowDefinitions>
<RowDefinition Height="70"/>
<RowDefinition Height="326*"/>
</Grid.RowDefinitions>
<Grid Grid.Row="0" Background="GhostWhite">
<Image Source="Assets/logo.png"/>
</Grid>
<ScrollViewer HorizontalAlignment="Stretch" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto" Grid.Row="1">
<StackPanel x:Name="Menu" Margin="10"/>
</ScrollViewer>
</Grid>
</Grid>
</Window>
This is the MainWindow.xaml.vb file:
Imports MaterialDesignThemes.Wpf
Imports Project.ViewModel
Partial Public Class MainWindow
Inherits Window
Public Sub New()
InitializeComponent()
Dim menuRegister = New List(Of SubItem)()
menuRegister.Add(New SubItem("Customer"))
menuRegister.Add(New SubItem("Providers"))
menuRegister.Add(New SubItem("Employees"))
menuRegister.Add(New SubItem("Products"))
Dim item6 = New ItemMenu("Register", menuRegister, PackIconKind.Register)
Dim menuSchedule = New List(Of SubItem)()
menuSchedule.Add(New SubItem("Services"))
menuSchedule.Add(New SubItem("Meetings"))
Dim item1 = New ItemMenu("Appointments", menuSchedule, PackIconKind.Schedule)
Dim menuReports = New List(Of SubItem)()
menuReports.Add(New SubItem("Customers"))
menuReports.Add(New SubItem("Providers"))
menuReports.Add(New SubItem("Products"))
menuReports.Add(New SubItem("Stock"))
menuReports.Add(New SubItem("Sales"))
Dim item2 = New ItemMenu("Reports", menuReports, PackIconKind.FileReport)
Dim menuExpenses = New List(Of SubItem)()
menuExpenses.Add(New SubItem("Fixed"))
menuExpenses.Add(New SubItem("Variable"))
Dim item3 = New ItemMenu("Expenses", menuExpenses, PackIconKind.ShoppingBasket)
Dim menuFinancial = New List(Of SubItem)()
menuFinancial.Add(New SubItem("Cash flow"))
Dim item4 = New ItemMenu("Financial", menuFinancial, PackIconKind.ScaleBalance)
Dim item0 = New ItemMenu("Dashboard", New UserControl(), PackIconKind.ViewDashboard)
Menu.Children.Add(New UserControlMenuItem(item0))
Menu.Children.Add(New UserControlMenuItem(item6))
Menu.Children.Add(New UserControlMenuItem(item1))
Menu.Children.Add(New UserControlMenuItem(item2))
Menu.Children.Add(New UserControlMenuItem(item3))
Menu.Children.Add(New UserControlMenuItem(item4))
End Sub
End Class
This is the ItemMenu Class:
Imports MaterialDesignThemes.Wpf
Namespace ViewModel
Public Class ItemMenu
Public Sub New(ByVal header As String, ByVal subItems As List(Of SubItem), ByVal icon As PackIconKind)
header = header
subItems = subItems
icon = icon
End Sub
Public Sub New(ByVal header As String, ByVal screen As UserControl, ByVal icon As PackIconKind)
header = header
screen = screen
icon = icon
End Sub
Public Property Header As String
Public Property Icon As PackIconKind
Public Property SubItems As List(Of SubItem)
Public Property Screen As UserControl
End Class
End Namespace
This is the SubItem Class:
Namespace ViewModel
Public Class SubItem
Public Sub New(ByVal name As String, ByVal Optional screen As UserControl = Nothing)
name = name
screen = screen
End Sub
Public Property Name As String
Public Property Screen As UserControl
End Class
End Namespace
This is the UserControlMenuItem.xaml file:
<UserControl x:Class="UserControlMenuItem"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
mc:Ignorable="d" >
<Grid>
<materialDesign:PackIcon Kind="{Binding Path=Icon}" Width="15" Height="15" Margin="10 16" Foreground="White"/>
<ListBoxItem x:Name="ListViewItemMenu" Content="{Binding Path=Header}" Padding="37 14" FontSize="15" Foreground="White"/>
<Expander x:Name="ExpanderMenu" Header="{Binding Path=Header}" IsExpanded="False" Width="210" HorizontalAlignment="Right" Background="{x:Null}" Foreground="White">
<ListView x:Name="ListViewMenu" ItemsSource="{Binding Path=SubItems}" Foreground="White" ScrollViewer.HorizontalScrollBarVisibility="Disabled">
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=Name}" Padding="20 5"/>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</Expander>
</Grid>
This is the UserControlMenuItem.xaml.vb file:
Imports Project.ViewModel
Partial Public Class UserControlMenuItem
Inherits UserControl
Public Sub New(ByVal itemMenu As ItemMenu)
InitializeComponent()
ExpanderMenu.Visibility = If(itemMenu.SubItems Is Nothing, Visibility.Collapsed, Visibility.Visible)
ListViewItemMenu.Visibility = If(itemMenu.SubItems Is Nothing, Visibility.Visible, Visibility.Collapsed)
Me.DataContext = itemMenu
End Sub
End Class
This is the Window when the app is running:
What I'm missing here?
Design cloned from DropDownMenu

Answer 1

I solved this problem. It was a detail I didn't realise. These are the corrected Classes:
The ItemMenu Class:
Imports MaterialDesignThemes.Wpf
Namespace ViewModel
Public Class ItemMenu
Public Sub New(ByVal header As String, ByVal subItems As List(Of SubItem), ByVal icon As PackIconKind)
Me.Header = header
Me.SubItems = subItems
Me.Icon = icon
End Sub
Public Sub New(ByVal header As String, ByVal screen As UserControl, ByVal icon As PackIconKind)
Me.Header = header
Me.Screen = screen
Me.Icon = icon
End Sub
Public Property Header As String
Public Property Icon As PackIconKind
Public Property SubItems As List(Of SubItem)
Public Property Screen As UserControl
End Class
End Namespace
The SubItem Class:
Namespace ViewModel
Public Class SubItem
Public Sub New(ByVal name As String, ByVal Optional screen As UserControl = Nothing)
Me.Name = name
Me.Screen = screen
End Sub
Public Property Name As String
Public Property Screen As UserControl
End Class
End Namespace
Just remained make reference to the Class with "Me" (self in other languages like Python) and then assign a value to the property:
Me.Header = header 'Example in ItemMenu Class
Me.Name = name 'Example in SubItem Class